1. Field of the Invention
This invention relates to a laser welding apparatus, a gas shielding apparatus and a method for controlling a laser welding apparatus.
2. Description of Related Art
A laser welding technique uses a laser beam having a high energy density of 105-106W/cm2 equal to that of an electron beam. Since the laser welding technique also uses a rapid heating process and requires only tenth energy power to be put in members to be welded in comparison with other welding techniques, it does not thermally deform the member and almost never thermally influences the member. Therefore, the laser welding technique can precisely weld the member made of a metallic material at a high speed under an atmospheric air. Particularly, in the laser welding technique using a YAG laser, since the YAG laser beams are absorbed into the members to be welded at a high degree, the members can be welded efficiently. And, since the laser beams can be transmitted by an optical fiber, the YAG laser welding technique can have large degree of freedom in its welding position and its welding configuration. In view of the above advantages, the laser welding technique is regarded as a promising welding technique in fabricating a structural body precisely.
However, although the laser welding technique has the above advantages, up to now, the laser welding technique is almost never adapted for the fabrication of the structural body due to the following reasons:
First of all, in comparison with a mechanical joining technique using bolts and nuts, the laser welding technique can fabricate a small structural body through its welding, and enhance the fabrication efficiency, but it has complicate weld processing phenomena, so that it is difficult to judge welding quality in the laser welding technique by visual inspection. Therefore, a nondestructive test or a destructive test using various equipment is required, and sometimes, durability evaluation or environment-resistance evaluation is required. As a result, the laser welding technique takes much time in the evaluation of the welding quality.
Moreover, in the laser welding technique, since the laser beams having spot diameters of not more than 1 mm are employed, the welded bead width becomes very small. Therefore, the clearance between the members to be welded must be controlled high precisely. In addition, since the welding quality may be influenced by the fluctuation in the sizes of the members to be welded and the slight difference in the weld processing condition, the sizes of the members and the weld processing condition must be monitored severely. Moreover, in the laser welding technique, since the laser beams to be used have small spot sizes, they must be moved along a seam line high precisely, and thus, the position of the laser beam must be controlled and determined high precisely. In view of the precise control and determination of the laser beam position, it is tried to make the parts to constitute the laser welding apparatus precisely and provide jigs on the laser welding apparatus. Moreover, it is also tried to feedback control the welding position by a sensor. However, the above means require large cost, and can not be applied for various purposes.
Moreover, although in the laser welding technique, the welding process can be carried out under an atmospheric air, which can not be performed in the electron beam welding technique, the atmospheric welding may form oxide films and segregation compounds at the welded parts of the members to be welded made of a metallic material through their oxidization. Therefore, if an ultrahigh-vacuum apparatus such as a scanning electron microscope or a spin electron microscope to observe a nm-order magnetic condition in a magnetic film is fabricated by the above atmospheric welding process, various gases may be emitted from oxide films and segregation compounds formed at the welded parts of the apparatus, and degrade the reliability of the apparatus. Accordingly, it is required to repress the formation of the oxide films and the segregation compounds to the minimum.
Conventionally, for preventing the formation of the oxide films and the segregation compounds, each part to be welded is set in a steel case, and thereafter, the steel case is evacuated and the laser welding process is performed in the steel case having anti-oxide shielding gas atmosphere. However, this conventional method requires large and complicate apparatus.
It is an object of the present invention to provide a laser welding apparatus, a gas shielding apparatus and a method for controlling a laser welding apparatus which can take advantage of the laser welding technique without the above-mentioned matters, and can be employed in fabricating such an ultrahigh-vacuum apparatus as a scanning electron microscope, a spin electron microscope or an electron spin analyzer to be attached the electron microscope.
For achieving the above object, this invention relates to a laser welding apparatus comprising a laser welding head and a laser welding head position-controlling apparatus,
the laser welding head including a laser irradiating body with an inert gas nozzle to blow off an inert gas for welding parts of members to be welded and at least one shielding gas nozzle, at the outside of the inert gas nozzle, to blow off a shielding gas for the surrounding area of the welding parts, and plural semiconductor lasers to oscillate plural linear laser beams for measuring the welding state of the members to be welded,
the laser welding head position-controlling apparatus including an imaging apparatus with a band-pass filter therein to pass through only the reflected linear laser beams to take in, as an image, the measured welding state by the reflected linear laser beams, and an image processor to process the image of the measured welding state.
Herein, the wording xe2x80x9csemiconductor laserxe2x80x9d also includes xe2x80x9csemiconductor light-emitting elementxe2x80x9d.
Moreover, this invention relates to a gas shielding apparatus for laser welding comprising an inert gas nozzle to blow off an inert gas for welding parts of members to be welded and at least one shielding gas nozzle, at the outside of the inert gas nozzle, to blow off a shielding gas for the surrounding area of the welding parts
Furthermore, this invention relates to a method for controlling a laser welding apparatus comprising the steps of:
irradiating plural linear laser beams for welding parts of members to be welded from plural semiconductor lasers provided on the laser welding apparatus,
accepting, as an image, the reflected linear laser beams from the welding parts into an imaging apparatus provided on the laser welding apparatus,
processing the image in an image processor provided on the laser welding apparatus,
calculating the state of the welding parts on the processed image, and
controlling a laser welding head provided on the laser welding apparatus.
As mentioned above, since the laser beams to be used in the laser welding technique have spot sizes of not more than 1 mm, the gap between both members to be welded must be appropriately monitored, and the positions of the laser beams must be determined precisely.
Generally, in the laser welding process, the gap width to be able to be welded is within 10% of the thickness of each member to be welded or within 50% of the focused spot size of the laser beam, and the precision of the laser position is within one-third of the focused spot size. Therefore, for the appropriate laser welding process, the gap width must be monitored at high precision, and the laser beam trace must be carried out along a seam line at a position precision of not more than {fraction (5/100)} mm. Moreover, the angle of the laser beam for the members to be welded and the height of the laser welding head must be controlled.
In the light of the above requirements, the laser welding head position-controlling apparatus is provided in the laser welding apparatus of the present invention. The laser welding head position-controlling apparatus includes the imaging apparatus with a band-pass filter therein and the image processor, and detects the welding state of the members to be welded such as a seam line trace, the height and the angle for the members to be welded.
Moreover, for reducing the calculation load of the welding state, it is desired to use CAD data for the members to be welded. That is, the shape and size of the crossing line or the crossing face between the members to be welded are calculated on the CAD data. On the other hand, the absolute position and angle of the laser welding head are calculated on the detected data. The CAD data and the detected data can be applied for NC data to perform the welding process. As a result, the operation time of the welding process can be shortened, and the reproducibility and the reliability of the welding process for the members having complicate shapes such as a sphere shape and a cylindrical shape can be enhanced.
Moreover, for preventing the formation of the oxide films and the segregation compounds in the welding process, a nozzle to blow off a shielding gas such as an anti-oxidizing gas in laminar flow for the welding parts of the members to be welded and its nearby parts is provided. In this case, since the welding process can be carried out while only the welding parts of the members to be welded are shielded almost perfectly against an outside air, the oxidization of the welding parts of the members can be prevented, and thus, the formation of the oxide films and segregation compounds can be repressed. As a result, a practical ultrahigh-vacuum apparatus and so on can be fabricated according to the present invention.